The NorthEastern portion of the United States is not particularly kind
to avid cyclists, especially those who work during prime daylight hours.
The electro-bike, herein referred to as E.B., was designed to keep the
user aerobically fit while creating some extra power that may be sent to
a bank of batteries that are mainly powered by photovoltaics. Any bicycle
will do. However, bicycles with wheels of larger diameters, such as 27
inches as opposed to 16 inches, create more mechanical advantage as will
be shown. Both street bikes, with very narrow, smooth tires, and mountain
bikes, with wide, knobby tires, have been used with equal success. The
bicycle is placed upon the stand, which is an Advent Mag-Trainer. It comes
assembled and folds up easily for transport - even after the alternator
is added.

Construction

First, we removed the roller and flywheel mechanism from the frame.
Two nuts and bolts hold the roller in place. Then, a metal plate, with
two holes drilled in it, was placed upon the bike standís swivel mount,
right under the rear wheel of the bike. This plate was 11 inches by 7 inches
and stiff enough to allow slight flexing. Two nuts and bolts were used
to secure the plate to the swivel mount. The alternator was mounted upon
this plate using four, two inch L brackets. There are two long bolts that
run through the alternator, horizontally when the alternator is on its
side. The L brackets can simply be fastened to these. It is not feasible
to have the axle of the alternator pressed up against the bikeís rear wheel
because massive slippage occurs. A small wheel needs to be fastened to
the alternatorís axle. Anything with a circumference between 2 and 10 inches
should do. The smaller the wheel, the greater the mechanical advantage,
but the more likely slippage is. I simply used the flywheel that came with
the stand. Since the alternatorís axle was too large to be fastened to
the flywheel, I had to grind the axle down. Hooking the alternator to a
12 volt battery and running it as a motor allowed the use of a file to
whittle down the axle to the proper size. Once this was accomplished, we
put the flywheel on the alternator and drilled a hole through the flywheel
mount and alternatorís axle to get a secure fit. A bolt was passed through
this hole and fastened with a lock washer and nut.

Operation

The bicycle is secured upon the stand by placing the E.B.ís back wheel
between the Advent standís two cup holders. A cycleís rear wheel has an
axle which terminates in a lug nut at each end. These lug nuts are to be
placed in each one of the cup holders. Then the cup holders are to be tightened
down on the lug nuts until the bicycle is held firmly. This also allows
perfect alignment (left to right) of the rear wheel directly above the
alternatorís wheel. Now the tension of the alternator mount needs to be
set. The knob under the metal plate changes the inclination of this plate
upon which the alternator is mounted. The adjustment knob should be tightened
so that you can hold the alternatorís wheel with one hand while trying
to spin the bikeís rear wheel with the other and get no slippage. Do not
overtighten. This will put undue stress on the components. It does not
take much tension to eliminate slippage. Since the rear wheel of the bike
is about one inch off the ground while in the stand, it may be necessary
to place a piece of wood under the front wheel. This will make the bike
level and prevent the rider from sliding forward on the seat while pedaling.
Keep in mind that the folks at Advent constructed this stand so that you
may easily remove a fully functional road bike and take it out for a spin
on a sunny day. Simply unscrew the holder cups from the lug nuts of the
E.B. and the bike easily comes away from the stand.

Math and Mechanics

The Univega Mountain Bike we used for most of the testing has 26 inch
wheels. This is the diameter of each wheel. The circumference is approximately
82 inches ( Circ. = PI * Dia. or 3.14 * 26 = 81.64). This fact is important
when deciding on the wheel you are going to use on the alternator. A wheel
with a circumference of 10 inches will spin 8.2 times faster than the bikeís
rear wheel ( 82/10 = 8.2). A wheel with a circumference of 4 inches yields
much more mechanical advantage ( 82/4 = 20.5 times). The faster the alternatorís
axle spins, the more amperage is available at the alternatorís output terminals.
I had no way of accurately measuring work exerted on the bike, but I tend
to spin a bikeís cranks at about 80 RPM using the large sprocket when I
am on the road. This large, front sprocket has 52 teeth and the smaller
sprocket on the rear wheel has 13 teeth, meaning the rear wheel spins 4
times faster than the cranks do. If the cranks are spinning at 80 RPM,
then the rear wheel is spinning at about 320 RPM. As shown before, the
rear wheel has a circumference of 82 inches to the flywheelís 10 inches.
The alternatorís axle spins 8.2 times faster than the rear wheel. So, the
rear wheel moving at 320 RPM means that the alternatorís axle is spinning
at about 2,624 RPM. This alternator speed consistently creates about 4
to 5 amperes of power. Crank speeds closer to 100 RPM create about 6 amps.
On sprints, I have watched the ammeter jump to almost 7 amps, but these
speeds are not sustainable, even for the disciplined athlete. The amperage
measurements were obtained by hooking an ammeter directly to the alternator.
Actual throughput will most certainly be less, especially when a charge
controller is used (see below).

Electrical Considerations

In the setup we constructed, the alternator is wired to a second charge
controller, which is wired in parallel with the main charge controller
and then run to the battery. If one were to use blocking diodes (I suggest
at least 10 ampere diodes) between the alternator and the main charge controller,
the alternator could be wired in parallel with the photovoltaics using
only a single charge controller. Two caveats: First, blocking diodes must
be used along the photovolatic power line to the charge controller BEFORE
this feed meets the alternator feed and then to the charge controller.
This is to prevent some of the alternatorís power running up to the panels
and being wasted as heat energy. Secondly, make sure this one charge controller
can handle full panel amperage PLUS the 7 amperes the electro-bike could
create at any one moment. My panels are able to create 6 amperes in strong
sun and the E.B. can crank out 7 amps on a real spin. Hence, a single charge
controller with a rating of less then 13 amperes could be troublesome if
it is very sunny at the same time the rider exhibits real zeal. Voltage
tends to be between 16 and 20 volts. Not very kind for direct connection
to a battery.

The Next Step

Recently, we have added a second alternator to the stand which doubles
the power output. I am searching for a larger alternator that would do
the work of two American Bosch alternators. Please note, that although
I have listed the supply house for the American Bosch alternator, they
no longer list this item in their catalog. I believe they still have some
in stock, though. All of this experimentation is a fine balance between
power creation and the strength required to turn the bikeís rear wheel.
The current configuration with one American Bosch alternator can be easily
spun by people of all ages. Larger alternators would be more difficult
to spin and might be feasible only for those looking to endlessly climb
imaginary hills. Finally, a cyclocomputer will be added that will measure
ground speed, time in training, average speed and top speed. This instrument
will be used primarily to compare the E.B. feel to that of a bike on a
road surface. If the average speed of the E.B. is much higher than that
of the bike on the road for a trip of the same length, then it can be deduced
that the E.B. is "too easy" and more load should be mated to
the E.B.ís rear wheel. Since there is no wind present when using the E.B.
indoors, additional resistance must be presented to the E.B.ís rear wheel
to experience a life-like ride.